1. Field of the Invention
This invention relates to maintaining and updating routing information in a packet switching network.
2. Description of Related Art
In routing messages in a computer network or in a network of networks (an "internetwork"), protocols for routing mes- sage packets generally provide two types of routes to a destination--static routes and dynamic routes. Static routes are preselected and configured before routing in a set of routing tables; typically this is performed manually. Dynamic routes are configured dynamically in response to routing information from other nodes; these routes require periodic updates (i.e., refreshes) of connectivity information, typically involving route refresh, adjacent node refresh, or other means.
One problem which has arisen in the art is that of intermittent connections--connections which are not continuously active, and for which lack of connectivity information refresh does not necessarily indicate that the connection has failed. For example, one type of intermittent connection is a dial-up link, such as used for dial-on-demand routing. For these communication links, it is generally undesirable and sometimes impossible to have routing and connectivity updates transmitted continuously. For example, in dial-on-demand routing, it is not generally possible to communicate routing and connectivity updates when the dial-up link is inactive.
One known method of treating dial-on-demand routing has been to statically configure the remote router with routing information indicating which devices can be located through a particular port (often a serial dial-up link) on the remote router. When a packet arrives at the remote router destined for one or more such devices, then the dial-up link is activated. Because the dial-up link can access a large number of devices at a large number of sites, large static tables are required. Static tables must be updated either manually or through periodic downloading of information in response to manual requests. Such manual management of these static tables is a significant task.
Known routing protocols (such as distance vector algorithms or link state algorithms) utilize dynamic routing updates and therefore cannot generally accommodate intermittent connections. These protocols "age" routing or connectivity information--if a device advertising the route is not heard from for a preselected time interval, existing routing protocols presume that the routes through the device are no longer available using that device, and the routing tables are updated accordingly.
Accordingly, it would be advantageous to provide a method and system in which routes including intermittent connections enjoyed the best aspects of both dynamic routes and static routes. Ideally, such routes and connectivity information could be dynamically updated using known protocol techniques for dynamic routes, but would not age during times when routing or connectivity information was not available for those connections.